The present invention relates to a method of serving induction coils with protective bands, as well as to an apparatus for accomplishing the method.
The principle of electrical induction heating is very well known, and electrical induction heating has found a widespread application in various fields of human endeavor, among others also in foundries. So, for instance, in the latter field, electrical induction coils may be used in crucible furnaces in which the induction coil is incorporated into the walls of the furnace which defines the chamber in which the metal is to be melted, heated and/or otherwise treated. Inasmuch as such crucible furnaces have substantial dimensions it will be appreciated that the induction coil used in such a furnace will also have substantial dimensions. So, for instance, such an induction coil may have an axial length of up to or even more than 2 meters, and may consist of more than sixteen convolutions, depending on the circumstances and on the design requirements. It is well known that the individual convolutions of the induction coil ought to be provided with a protective layer, particularly for the purpose of electrical insulation. For this purpose it is already known to serve the convolutions of the induction coil with a protective band which is wrapped around the convolutions of the induction coil in a helical manner and in one or more layers. In either event, a single band can be served upon the convolutions, or a plurality of such protective bands either of the same material and properties or of different materials and properties. When the desired goal is electrical insulation of the convolutions of the induction coil, it is advantageous to use a band of fiber glass fabric.
The method of serving the protective band or bands onto the convolutions of the induction coil which is prevelant today consists of manually wrapping the band about the convolutions, which is considerably time-consuming and, consequently, expensive owing to the high cost of the labor involved. The factors which make this manual procedure very costly are the substantial dimensions of the induction coil, the fact that the induction coil consists of a plurality of adjoining convolutions which form a continuous helix, and that the induction coil is usually formed by winding the profiled element having a substantial cross section, possibly of tubular configuration, into the helical shape of the induction coil. The material of the induction coil is electrically conductive and, more often than not, consists of copper or of an alloy including a substantial proportion of copper. The individual convolutions of the induction coil are usually closely adjacent to one another in the axial direction of the induction coil.
There is already known a method of and an apparatus for wrapping a protective band around annular or toroidal bodies of different shapes and serving various purposes. One conventional apparatus for performing this conventional method includes an automatic or a semi-automatic serving machine which includes a bench and a split housing mounted on the bench, a split serving ring being mounted in the split housing for rotation about the respective annular or toroidal body to be provided with the protective layer. The body is introduced into the housing and into the serving ring through the split portion of the housing and through the split portion of the ring. In this known apparatus the slot through which the body is introduced faces toward the bench. The serving ring supports a payout reel or roll accommodating the band of protective material, the reel rotating together with the serving ring about the portion of the body to which the band is to be applied, and also revolving about its own axis as the protective band is payed out. Attempts have already been made to use such an apparatus for serving the protective tape onto the convolutions of an induction coil or to modify this existing apparatus so as to be capable of serving the protective band on such convolutions of the induction coil. However, such attempts have met only with a limited success and the modifications were too extensive and expensive. One of the main problems with this modified apparatus was that it required relatively complicated guiding systems by means of which the adjacent convolutions of the induction coil were, in continuous succession, first axially spread away from one another and, subsequent to the winding operation, against pressed axially toward one another, during the relative rotation and simultaneous axial displacement of the induction coil with respect to the housing of the serving apparatus which was arranged stationarily in a vertical plane. An additional problem encountered in serving the protective band onto the convolutions of a helical induction coil, as compared to serving the band on simple annular or toroidal bodies, resides in the fact that the induction coil is equipped with electrical terminals and also, in the region of each third or fourth convolution, with projecting outlet nipples for the introduction and withdrawal of a cooling medium to and from the interior of the induction coil for the purpose of cooling the coil during the operation thereof. These terminals and nipples extend a substantial distance radially outwardly from the outer periphery of the respective convolution and they represent a considerable obstruction to the faultless performance of the serving operation. First of all, such radially outstanding portions of the induction coil prevent secure guidance of the convolutions of the coil on the usually horizontally extending bench, and the spatial guidance of the convolutions, or at least make such connection to the bench and such guidance very difficult. However, more importantly, these radially extending portions make it impossible to use stationarily mounted serving housings in which the slots which permit the introduction of the convolution into the interior of the housing are directed toward the bench.
In order to avoid this disadvantage, it would be conceivable to utilize a differently configurated serving housing which would be mounted for infinite adjustment of its position. However, even if the serving apparatus were so modified, this would not simplify to any considerable extent the complicated guidance of the convolutions of the induction coil but, on top of it, it would require an additional guiding arrangement for the infinite displacement of the serving ring housing, which would be at least just as complex.
An additional problem is to be seen in the fact that such an apparatus of a conventional construction would only be economically feasible if it was not tailored to only one predetermined diameter of the induction coil and to one predetermined cross section of the convolutions thereof. In other words, the investment in such apparatus would bring in the desired return only if the apparatus could be adapted in a simple manner to serving the protective band onto the convolutions of differently shaped induction coils. This additional requirement renders the guiding systems, which are complex as it is, even more complicated and, consequently, more expensive.
As a result of all of the above-mentioned problems, the induction coils of this type are presently, as previously, served with the protective band manually, even though it would be desirable to accomplish at least semi-automation of the serving operation, especially for coils having large diameters and a great number of convolutions, particularly in view of the labor and time expenditures which would be saved through the automation or semiautomation of this operation.